Theoretical Study on the Degradation Pathways of Unsymmetrical Dimethylhydrazine by Aqueous O 3

Air discharge plasma is a potential method for the removal of the toxic rocket propellant unsymmetrical dimethylhydrazine ((CH 3 ) 2 NNH 2 , UDMH for abbreviation). Combining density functional theory calculation and transition state theory, this paper presents theoretical investigation of the degradation pathways of UDMH under the influence of O 3 in aqueous environment, which is the main reactive species generated by air plasma. The neutral, protonated and deprotonated forms of UDMH are included in our study considering the effect of pH. The results show that the UDMH degradation by O 3 usually initials with the oxygen addition to the N atom, and the reaction positions would change with the pH variation. The main reaction position of neutral and protonated forms of UDMH are the N atom of primary ammonia of UDMH, where UDMH will be converted into N-nitrosodimethylamine and NH 2 OH through multi-step reactions. For deprotonated UDMH, its main reaction position changes to the N atom of secondary ammonia of UDMH, and it finally decomposes to (CH 3 ) 2 NN and OH with the rate constant of 8.26 × 10 3 M −1 s −1 . The pH value also largely influences the degradation processes, where the rate constants of corresponding reactions would vary by up to 12 orders of magnitude for different forms of UDMH. Based on our calculation, the main byproducts of UDMH degradation and their subsequent degradation pathways are summarized. This work is helpful to lay the theoretical basis of UDMH degradation by plasma ozonation.